Challenge EMT in CA?

I would suggest it's going to be difficult challenging the exam because there's a lot of stuff your LVN training didn't cover that EMT's are required to know.

For example:

What does the letter S stand for in DCAPBTLS?

The O in OPQRST stands for?

During blast trauma the tertiary blast phase would likely cause injury by?

After applying a cervical collar to a patient and securing them to the backboard what must you check before transporting them?

Which laryngoscope blade would you choose when intubating a child?

...Was any of that subject matter covered in your LVN training?

To get all the required knowledge and practical hands on experience you need to complete the exam, it's probably easier to just simply enroll in an EMT course.

Some of the community colleges, like Palomar for instance, have accelerated EMT programs. I think I completed the whole thing over a Summer and they may have a Winter break one as well. You'd have to figure out if this is doable with your schedule and compete to get in. ER's typically want previous experience such as on an ambulance.

Hopefully there is an easier route where you can just study up and challenge the test. You can contact the community college EMS secretaries and ask. Honestly though, if you have to go back through that many units of schooling plus experience (as sort of a glorified taxi driver), why not just enroll in an LVN to RN program and work your way to being an ER nurse? 6 cheap units going backwards or 30 expensive units going forward.